A non-contact power feeding apparatus transmits, by at least magnetic coupling, an electric power in a non-contact manner to a power reception coil from a power transmission coil. The transmission coil is electrically connected to an alternating-current power source. The non-contact power feeding apparatus outputs an electric power to a load electrically connected to the power reception coil. The non-contact power feeding apparatus includes a coupling state estimator configured to estimate a coupling state between the power transmission coil and the power reception coil. The non-contact power feeding apparatus also includes an available output power calculator configured to calculate an available output power that can be output to the load, based on a limit value of a circuit element of a power feeding circuit including the power transmission coil and the power reception coil and on the coupling state.
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1. A non-contact power feeding apparatus which transmits, by at least magnetic coupling, an electric power in a non-contact gunner to a power reception coil from a power transmission coil electrically connected to an alternating-current power source and which outputs an electric power to a load electrically connected to the power reception coil, the non-contact power feeding apparatus comprising: a coupling coefficient estimator configured to estimate a coupling coefficient between the power transmission coil and the power reception coil; and an available output power calculator configured to calculate an available output power that can be output to the load, based on a limit value of a circuit element of a power feeding circuit including the power transmission coil and the power reception coil and on the coupling coefficient.
A wireless power transfer system transmits power from a source coil connected to an AC power supply to a receiver coil connected to a load. It estimates the coupling coefficient between the two coils, and calculates the maximum available output power that can be safely delivered to the load. This calculation is based on the coupling coefficient and the current/voltage limits of components within the power transfer circuit (including the transmitting and receiving coils), ensuring that no component exceeds its rated limits during power transfer.
2. The non-contact power feeding apparatus according to claim 1 , wherein from a relationship expressed by a theoretical formula including an inductance of the power transmission coil, an inductance of the power reception coil, a drive frequency of the alternating-current power source, the coupling coefficient, and a current or voltage of the circuit element, the available output power calculator calculates the available output power using the coupling coefficient estimated by the coupling coefficient estimator and the limit value.
The wireless power transfer system calculates the available output power using a theoretical formula. This formula incorporates: the inductance of the transmitting coil, the inductance of the receiving coil, the drive frequency of the AC power source, the coupling coefficient between the coils (as estimated by a coupling coefficient estimator), and the maximum current or voltage limit of a component in the circuit. The system then uses this formula, along with the estimated coupling coefficient and circuit element limits, to determine the available output power.
3. The non-contact power feeding apparatus according to claim 1 , further comprising: a command value generator configured to generate a command value of a power converter for outputting the available output power to the load, based on the available output power, wherein the power converter is provided in the alternating-current power source, and converts an input electric power and outputs the converted electric power to the power transmission coil.
The wireless power transfer system includes a command value generator. Based on the calculated available output power, this generator creates a command value for a power converter located in the AC power source. This power converter takes an input power and converts it before supplying it to the transmitting coil. The command value regulates the power converter to output power suitable for delivering the maximum available output power to the load, controlling the power transfer process.
4. The non-contact power feeding apparatus according to claim 3 , further comprising: an error range calculator configured to calculate an error range in the coupling coefficient, due to an estimation error of the coupling coefficient estimator, wherein the available output power calculator calculates the available output powers based on a plurality of coupling coefficients included in the error range, respectively, and wherein the command value generator generates the command value based on a smallest available output power among the calculated plurality of available output powers.
The wireless power transfer system calculates a possible error range for the coupling coefficient due to inaccuracies in its estimation. The system calculates the available output power for several different coupling coefficient values within this error range. It then selects the *smallest* of these calculated available output powers and uses it to generate the command value for the power converter. This ensures that the power delivered to the load never exceeds the safe limit, even with estimation errors of the coupling coefficient.
5. The non-contact power feeding apparatus according to claim 3 , further comprising: an error range calculator configured to calculate an error range in the coupling coefficient, due to an estimation error of the coupling coefficient estimator; a sensor that detects a voltage or current of the power feeding circuit; and a determiner configured to determine, based on a detection value of the sensor, which of a first range corresponding to a range between an intermediate value in the error range and a lower limit value in the error range or a second range corresponding to a range between the intermediate value and an upper limit value in the error range an actual electric power that can be output to the load belongs to, wherein the command value generator generates the command value in accordance with a determination result of the determiner.
The wireless power transfer system calculates an error range for the coupling coefficient and also uses a sensor to detect the actual voltage or current in the power transfer circuit. A determiner then decides whether the actual power level is in the lower half or the upper half of the error range. Based on this determination, the system generates a command value. It selects different command values depending on whether the true power is likely to be in the lower or upper portion of the coupling coefficient error range.
6. The non-contact power feeding apparatus according to claim 5 , wherein when the actual electric power that can be output to the load belongs to the first range, the command value generator generates the command value based on a smallest available output power among the calculated plurality of available output powers.
In the wireless power transfer system described in Claim 5, if the determiner determines that the actual output power is in the *lower* range of the possible output power (based on the coupling coefficient error range), then the command value generator uses the *smallest* calculated available output power (as determined by the range of possible coupling coefficients) to generate the command value. This prioritizes safety and avoids exceeding component limits.
7. The non-contact power feeding apparatus according to claim 5 , wherein when the actual electric power that can be output to the load belongs to the second range, the command value generator generates the command value based on the available output power calculated from a coupling coefficient of the intermediate value.
In the wireless power transfer system described in Claim 5, if the determiner determines that the actual output power is in the *upper* range of the possible output power (based on the coupling coefficient error range), then the command value generator uses the available output power calculated using the *intermediate* coupling coefficient value (the middle of the error range) to generate the command value. This allows for more efficient power transfer when the true power level is likely higher.
8. The non-contact power feeding apparatus according to claim 3 , further comprising: a detector configured to detect an input voltage and input current to the power feeding circuit from the power converter, wherein the command value generator generates an estimation command value that is the command value for estimating the coupling coefficient, and outputs the same to the power converter, and wherein the coupling coefficient estimator estimates, in a state where a drive frequency of the power converter and a resonant frequency of the power feeding circuit are matched, the coupling coefficient based on the input voltage of the power converter being driven with the estimation command value, the input current of the power converter being driven with the estimation command value, and a resistance of the load.
The wireless power transfer system has a detector to measure the input voltage and current supplied *to* the power transfer circuit *from* the power converter. The system generates a special "estimation command value" specifically designed to estimate the coupling coefficient. The coupling coefficient estimator then operates when the power converter's drive frequency is matched to the resonant frequency of the power transfer circuit. It calculates the coupling coefficient using the measured input voltage, input current, and the load resistance while driven by this estimation command value.
9. The non-contact power feeding apparatus according to claim 8 , wherein from a relationship expressed by a theoretical formula including an inductance of the power transmission coil, an inductance of the power reception coil, the input voltage, the input current, a resistance value of the load, and the drive frequency of the power converter, the coupling coefficient estimator estimates the coupling coefficient using an input voltage of the power converter being driven with the estimation command value and an input current of the power converter being driven with the estimation command value.
The coupling coefficient estimator of the wireless power transfer system from Claim 8 calculates the coupling coefficient using a theoretical formula. This formula uses the input voltage and current to the power converter (measured while driven by the special estimation command value), the load resistance, the drive frequency, the transmitting coil inductance, and the receiving coil inductance. These values are plugged into the formula to determine the coupling coefficient.
10. The non-contact power feeding apparatus according to claim 8 , further comprising: an adjustment circuit including a resistor for matching a resonant frequency of a resonant circuit on a secondary side of the power feeding circuit with the drive frequency and a switch unit configured to switch ON and OFF between the resistor and the power reception coil, wherein the coupling coefficient estimator estimates the coupling coefficient, in an ON-state of the switch unit.
The wireless power transfer system from Claim 8 includes an adjustment circuit with a resistor and a switch. This circuit is used to match the resonant frequency on the receiving side of the power transfer system to the drive frequency. The switch toggles the connection between the resistor and the receiving coil. The coupling coefficient estimator performs its estimation *when the switch is ON*, meaning the resistor is actively part of the receiving-side resonant circuit.
11. The non-contact power feeding apparatus according to claim 8 , further comprising: a resonant circuit for matching a resonant frequency on a secondary side of the power feeding circuit with the drive frequency; and a switch unit configured to switch ON and OFF between the resonant circuit and the power reception coil, wherein the coupling coefficient estimator estimates the coupling coefficient, in an ON-state of the switch unit.
The wireless power transfer system from Claim 8 has a resonant circuit for matching the resonant frequency on the receiving side to the drive frequency, and a switch that connects or disconnects the resonant circuit from the receiving coil. The coupling coefficient estimator estimates the coupling coefficient *when the switch is ON*, meaning the resonant circuit is actively connected to the receiving coil and influencing the power transfer characteristics during the estimation process.
12. The non-contact power feeding apparatus according to claim 3 , further comprising: a first detector configured to detect a voltage, current, or power of a circuit on a power reception side in the power feeding circuit; and a coupling coefficient calculator configured to calculate the coupling coefficient based on a detection value of the first detector, wherein the available output power calculator calculates a first available output power that can be output to the load, based on a coupling coefficient estimated by the coupling coefficient estimator, and calculates a second available output power that can be output to the load, based on a coupling coefficient calculated by the coupling coefficient calculator, and wherein the command value generator generates a first command value based on the first available output power to control the power converter, and then generates a second command value based on the second available output power to control the power converter.
The wireless power transfer system includes a detector on the receiving side of the circuit to measure voltage, current, or power. It also has a coupling coefficient calculator that uses these measurements to calculate a coupling coefficient. The system then calculates *two* available output powers: one using the coupling coefficient estimated by the primary estimator (based on the transmitting side), and another using the coupling coefficient calculated from the receiving-side measurements. The command value generator first uses the first available output power and then switches to using the second available output power to control the power converter.
13. The non-contact power feeding apparatus according to claim 12 , wherein: the coupling coefficient estimator estimates the coupling coefficient based on detection information of a detection value of a sensor provided on a power transmission side, and the command value generator increases the first command value and the second command value at a predetermined cycle, and an amount of change in the second command value per the cycle is larger than an amount of change in the first command value per the cycle.
In the wireless power transfer system from Claim 12, the primary coupling coefficient estimator uses sensor data from the transmitting side. The command value generator increases both the first command value (based on the transmitting side estimate) and the second command value (based on the receiving side calculation) at a regular interval. However, the *amount of change* in the second command value (based on receiving side) is *larger* than the amount of change in the first command value (based on transmitting side) for each interval.
14. The non-contact power feeding apparatus according to claim 12 , wherein the command value generator increases the second command value in a stepwise manner.
In the wireless power transfer system from Claim 12, the second command value (the one based on the coupling coefficient calculated from measurements on the receiving side) is increased in discrete steps, rather than smoothly, to adjust the power output.
15. The non-contact power feeding apparatus according to claim 12 , further comprising: a second detector configured to detect a voltage or current of the circuit element; and a usage rate calculator configured to calculate a usage rate expressed by a ratio of a detection value of the second detector relative to the limit value, wherein the command value generator keeps the command value, when the usage rate becomes equal to or greater than a first limit value that is set in order to maintain a power-feeding performance of the non-contact power feeding apparatus or in order to protect the circuit element.
The wireless power transfer system includes a second detector to measure voltage or current in a circuit element and a usage rate calculator that determines the ratio of the measured value to the component's limit. The command value generator *holds the command value steady* if this usage rate exceeds a pre-defined first limit. This limit is set to either maintain the overall performance of the wireless power transfer system or to protect specific circuit elements from damage due to excessive current/voltage.
16. The non-contact power feeding apparatus according to claim 12 , further comprising: a second detector configured to detect a voltage or current of the circuit element; and a usage rate calculator configured to calculate a usage rate expressed by a ratio of a detection value of the second detector relative to the limit value, wherein the command value generator keeps, when the usage rate becomes equal to or greater than a second limit value that is set in accordance with a detection error f the second detector or a variation in manufacturing the circuit element, a command value that is generated before the usage rate reaches the second limit value.
The wireless power transfer system has a second detector to measure voltage or current in a circuit element and a usage rate calculator which determines the ratio of the measured value to the component's limit. If the usage rate exceeds a second limit (which is determined based on potential measurement errors and manufacturing variations), the system *maintains the command value that was in place just *before* the usage rate reached the second limit*. This is a safety mechanism to account for uncertainties in the measurements or components.
17. The non-contact power feeding apparatus according to claim 3 , further comprising: an error range calculator configured to calculate an error range in the coupling coefficient, due to an estimation error of the coupling coefficient estimator; and a divider configured to divide an available output power range into a plurality of available output power ranges, wherein the available output power calculator calculates the available output powers based on a plurality of coupling coefficients included in the error range, respectively, thereby calculating the available output power range corresponding to the error range, and wherein the command value generator generates, in order from a smaller available output power range among the plurality of available output power ranges divided by the divider, the command value based on the available output power included in the available output power range, and outputs the command value to the power converter.
The wireless power transfer system calculates an error range for the coupling coefficient and divides the potential output power range into smaller ranges. The available output power calculator determines the full range of available output powers based on the coupling coefficient error range. The command value generator then starts by generating command values based on the *smallest* available output power range and sequentially increases the command value through the other ranges.
18. A non-contact power feeding method for transmitting, by at least magnetic coupling, an electric power in a non-contact manner to a power reception coil from a power transmission coil electrically connected to an alternating-current power source and for outputting an electric power to a load electrically connected to the power reception coil, the method comprising: estimating a coupling coefficient between the power transmission coil and the power reception coil; and calculating an available output power that can be output to the load, based on a limit value of a circuit element of a power feeding circuit including the power transmission coil and the power reception coil and on the coupling coefficient.
A method for wirelessly transferring power from a source coil connected to an AC power supply to a receiver coil connected to a load. The method involves estimating the coupling coefficient between the transmitting and receiving coils. The method then calculates the maximum available output power that can be safely delivered to the load. This calculation is based on the coupling coefficient and the current/voltage limits of components within the power transfer circuit (including the transmitting and receiving coils), ensuring that no component exceeds its rated limits during power transfer.
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March 5, 2013
October 31, 2017
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